At present most of the lamps used in street lighting on the market are conventional mercury vapor lamps, which are fitted in the sockets of the street lights and illuminate streets. It is known that these conventional mercury lamps have a shorter lifespan less than 3,000 hours. Besides, they still have various other disadvantages, such as big energy consumption, high operation cost, etc. It is obvious that the conventional mercury vapor lamps have no longer been able to satisfy the requirements of energy conservation and pollution reduction in the modern society.
On the other hand, today the rapid developing light emitting diode (LED) illumination technology has provided a reasonable alternative for street lighting, which replaces the widely used mercury vapor lamps with LED lamps for higher energy utilization efficiency. However, the existing street lights have been developed for more than a century; a firmed industrial standard has been formed. For example, the socket widely used in street lights for receiving the lamp is a metal cap-shaped connector named E40. For replacing the conventional mercury vapor lamps with LED lamps, the best plan is to connect LED lamps directly to the sockets of the existing street lights without any modifications. However, this cannot be realized now because the current LED lamps have not had the specific connectors (e.g. E40 metal cap) as the conventional lamps. Moreover, most of the LED lamps tend to have a compact structure to reduce the weight and volume. This structure directly results in a smaller interior space, thus in such a small room, the ability of heat-dissipating will be significantly weakened, and consequently becomes an important problem studied by people.